Digital-to-analogue convertors



Dec. 26, 1967 NAOKAZU K|MURA 3,360,7924

DIG ITAL-TO-ANALOGUE CONVERTORS Filed Oct. 16, 1964 4 Sheets-Sheet l ATTORNEY *IDEC 26, 1967 NAoKAzu KIMURA `3,360,792

DIG ITAL-TO-ANALOGUE CONVERTORS Filed Oct. 16. 1964 y 4 Sheets-Sheet 2 F/G. 3 DE Q0 l 1| i l l f I O l Reference A. C. f VO/age /Nvf/vrae )ma zaza M/M wea ATTORNEY Dec. 26, 1967 NAoKAzu KIMURA DIGITAL-TO-ANALOGUE CONVER'IORS 4 Sheets-Sheet 3 Filed Oct. 16. 1964 ATTORNEY Dec. 26, 1967 I NAOKAZU KIMURA 3,360,792

I DIGITAL-TO-ANALOGUE CONVERTORS Filed Oct. 16. 1964 4 Sheets-Sheet 4 ATTORNEY United States Patent O N' 3,360,792 DIGlTAL-TO-ANALOGUE CONVERTQRS Naokazu Kimura, Katsuta-shi, Japan, assigner to Hitachi, Ltd., Tokyo, Japan, a corporation of Japan Filed Oct. 16, 1964, Ser. No. 404,231 1 Claim. (Cl. 340-347) liability, and longer in useful life than those having movable elements.

A further object of the present invention is to provide a vD-A convertor capable of dealing with digital input signals either of plus or minus signs for supplying output signals ofv analogue quantities having corresponding characteristics.

j A still further object of the present invention is to provide a D-A convertor consisting of transformers and electronic switches, such as transistor, semi-conductor devices with control electrode and etc.

A further object Vof the present invention is to provide a D-A convertonwithrelatively low output impedance and large-output power by .virtue of use of transformers.

There are other objects and particularities of the present invention, which will be made obvious from the following detailed description of the invention, with reference to the accompanying drawings, in which:

FIG. 1 is fa block diagram showing one embodiment of the invention;

FIG. 2v is a block diagram showing the digital-to-phase convertor shown in FIG. 1.;

FIGS. 3 and`4 show examples of elementary circuit of the convertor shown in FIG..2;

FIGS. 5 and 6 show examples of A.C. current distributor, ofwhich that shown'in FIG. 5 obtains A.C. current by driving transistors from D C. standard voltage supply by means of A.C. oscillator;

FIG. 7 shows an example of synchronous rectifying circuit; a

FIGS, 8 and 9 show synchronous rectifying circuits with error compensation; and

FIGS. 10 and 11 show voltage v. phase relations, respectively, applied to transistors for improving output characteristics of the synchronous rectifying circuit.

A digital quantity X is here represented by [P0, P1, P2, .P11], wherein kP11 designates plus or minus sign of the digital quantity, and P1, P2, Pn designate number of places of the same. It is assumed here that P0, P1, P2, .Pn take, respectively, 0 or 1, and when P11: 1, the digital quantity is positive, while when P0=0 the digital quantity is negative.

Consequently, if a digital quantity X is represented by where=l,2, n.

The present invention provides means for converting digital quantities to analogue quantities, following to the conversion Equation 1.

3,360,792 Patented Dec'. 26, 1967 Referring now to FIG. 1, the D-A convertor shown comprises a digital-to-phase convertor 1, an A.C. voltage distributor 2, a number of synchronous rectifying circuit 30, 31, 32, 311, and an addition circuit 4.

The digital-to-phase convertor 1 is to generate A.C. output of phases represented by qu, q0q1, qgqz, qoqn from digital signal [Pm P1, P2, .P11]. The relation between q1 and P1 is given by the following Equation 3: Y

q1=2P1-1(z'=0, 1, 2, n) (3) As is known from the above equation, q1 is +1 or 1 corresponding to whether P1 is 1 or 0. In other words, the convertor 1 generates either positive phase or negative phase of A.C. voltage, corresponding to the above equation. Thus, the digital-tophase convertor 1 may be any known apparatus that provides output signal qu. 110611. floqi. 1 quan for digital input Signal (P0, P1.

2, Pn). v

FIG. 2 shows an example of digital-to-phase convertor by block diagram, whichpis constituted by a combination of elementary circuits for producing A.C. output of phase equal to the product of a digital signal and the phase of A.C. signal, from the digital quantity and the A.C. signal. l

A practical example of the elementary circuit is shown in FIG. 3, in which a switch SW is operated to convert the phase of A.C. signal qs to positive or negative phase according `to the value of P0. In-FIG. 4 is shown an elementary circuit useful for utilizing electronic switch` when the A.C. signal qs is of rectangular wave form, in which the switch SW is connected to the ground at one end, and current may be made to flow through the switch SW in one direction only.

The A.C. voltage distributor 2 is a circuitry for producing A.C. voltage having amplitude proportional to b1-l-b2-ibn and respective places b1, b2, bn. In the distributor shown in FIG. 5, in order to produce A.C. voltage of correctly constant amplitude, transistors 51 and 52 are driven by an A.C. oscillator 53, the A.C. current being obtained from a D.C. standard voltage Es. In place of transistors, electron valve, semi-conductor rectifying elements with control electrodes, etc., may be used to obtain A.C. current of similarly high output. The standard A.C. voltage thus produced may be distributed to output volt-ages proportional to b1, b2, bn, respectively, by use ofthe principle of transformer, by the number of turns N1, N2, Nn of respective coils.

As is shown in FIG. 6, the A.C. distributor circuit 2 may be constituted merely byva transformer, provided that the standard A.C. voltage can be obtained correct.

The synchronous rectifying circuits 30, 31, 32 311 serve to produce D.C. voltages, respectively, proportional in magnitudes to the outputs of A.C. Voltage distributor 2 and having plus or minus pola-rities corresponding to positive or negative phases of the outputs of digital-phase convertor 1.

In FIG. 7 is shown an example of the synchronous rectifying circuit employing transistors. The output from digital-phase convertor 1 is applied across input terminals 71 and 71', while the output from A.C. voltage distributor 2 is applied across input terminals 72 and 721', and the D.C. output appears across output terminals 73 and 73'. It is to be noted that the A.C. signals from digitalphase convertor land A.C. voltage distributor are in synchronism. It is also to be noted that, in pl-ace of transistors, electronic tubes, mercury rectiiiers, or semi-conductor rectiers with control electrodes, may similarly be used.

T he 'addition circuit 4 is for summation or composition of output voltages of synchronous rectifying circuits 311, 31, 311. As is understood from the foregoing example, synchronous rectifying circuits are easy to insulate for each other so that they may be connected merely in series. This is very advantageous from practical point of view. In ladder type of addition circuit, there is restraint in the code system of digital signals. For example, decoding of pure binary signals is easy to effect, but decoding of 1,2,2,4 codes, 1,l,2,5 codes is considered impossible. Contrary to the above, the series addition system has substantially no restraint, except that P0, P1, P2 Pn assumes O or 1.

' In summary, the .output voltage Y of D-A convertor is given by the following equation:

Substituting the relation of Equation 3 into the above,

By comparing-Equations 1 and 5 with each other, ai and b1 are co-related as follows:

Then

Thus, a D-A convertor is obtained for providing analogue voltage Y from digital input X.

In pnactical manufact-ure of the apparatus of present invention, some problems exist and they can be solved as follows:

(1) The A.C. voltage distributor 2 utilizes the fact that the output voltages are proportional to number of turns. This necessitates that all the coi-ls have to be interlinked by equal uxes. For this purpose, a toroidal magnetic core of good symmetry of least leakage flux should be employed for obtaining high precision.

(2) In the synchronous rectifying circuit as shown in FIG. 7, when the phase input is of rectangular Wave form, an oiTset D.C. voltage of a particular polarity appears across the D.C. output terminals, even when the output voltage of A C. voltage distributor is By virtue of such a voltage, when synchronous rectier output of reverse polarity is obtained by reversing the phase during operation, its absolute value must be erred. The circuit of FIG. 8 has been designed for eliminating such offset voltage. In this circuit, two sets of transistors having characteristics 'of good coincidence are used, so that offset voltages may cancel each other, not to appear across the output termin-als. In the arrangement shown in FIG. 9, a plurality of synchronous rectifying circuits are employed in the DA converter, and taking advantage of such an arrangement, two of them are connected to have their offset voltages in opposition to each other. This arrangement is advantageous in comparison to that of FIG. 8 in that the former lrequires less number of transistors.

(3) In the synchronous rectifying circuit of FIG. 7, when both of the output and the phase input of A.C. distributor are of rectangular wave for-ms and substantially in phase (or of opposite phases), with respect to digital value, D.C. output voltage might be bad in their linearity. This is considered due to the fact that the collector-base voltage and the collector-emitter voltage of the switching resistor in FIG. 7 vary in voltage and current values almost simultaneously, and there occurs a cert-ain sort of obscurity in the switching operation. For remedy of the same, there may be introduced a certain degree of phase displacement between the digital phase convertor output D and the A.C. distributor output A, as shown in FIG. 10, or as shown in FIG. 11, the output voltage wave form of A.C. distributor A may bemodied, so as not to have the two voltages changing.. simultaneously. By this, the linearity can be remarkably improved.

As has `been hereinabove described in detail, the new apparatus according tothe present invention can convert digital quantity of either positive or negative sign to analogue voltage having corresponding polarity,land by use of transformers, its output impedance is low. In addition,

if semi-conductor rectifying elements with control elec-' trodes, mercury rectitiers, or the like are utilized in place of switching transistors, D-A convertors of large capacity can be provided, so that the D-A convertors may directly. drive controlled members in automatic control apparatus and the like. There is no movable member, such as relay, involved in the present apparatus, and consequently, the present new apparatus is higher in operating speed and reliability, and longer in useful life than those necessitating movable elements.

What we claim is:

A digital-to-analogue convertor for converting a digital quantity of decimal, binary, or any other system, to an analogue quantity, characterized by comprising a digital-to-phase converting circuit lfor converting the positive and negative signs and number of places of said digital quantity into positive or negative phases of alternating current correspondingly, an A C. voltage distributor circuit for producing alternating current magnitudes corresponding respectively to significance of s-aid places of said digital quantity, synchronous rectifying circuits for generating D C. voltages of polarities and magnitudes which corresponds respectively to the output of said digital-to phase convertor and the output of said A.C. voltage distributor circuit, and an addition circuit for composing up said output voltages of said synchronous rectifying circuits.

No references cited.

DARYL W. COOK, Acting Primary Examiner.

i W. I. KOPACZ, Assistant Examiner. 

